The following relates to the nuclear power generation arts, nuclear reactor safety arts, nuclear reactor emergency core cooling (ECC) arts, and related arts.
In a loss of coolant accident (LOCA), the nuclear reactor core is to be kept immersed in water so as to provide for removal of decay heat and to prevent exposure of the fuel rods to air which can lead to chemical reactions and release of airborne radioactivity. The system which provides this water injection is referred to as the emergency core cooling (ECC) system. In a typical arrangement, a refueling water storage tank (RWST) is located with the nuclear reactor inside radiological containment to provide water for use during reactor refueling, and this RWST also serves as a water source for the ECC system. The RWST is located above the reactor core so that the passive ECC system can operate by gravity-driven water flow.
Water injected into the depressurized pressure vessel by the ECC system is converted to steam by decay heat from the nuclear reactor core. Preferably, this steam is recaptured by condensing it into the RWST so as to form a closed-loop recirculating heat exchange system. In practice, some steam is lost from the break that caused the LOCA. This lost steam condenses inside the surrounding radiological containment, thereby contributing to heat transfer from the reactor core although not in a recirculating fashion. In some embodiments, the water collects in a containment sump, and a sump pump is provided to recirculate the water back into the RWST. However, this approach is susceptible to failure if the diesel generators or other power source driving the sump pump fail, and moreover there is the potential to transfer contamination into the RWST that can interfere with operation of the ECC system.